This invention relates to nitrogen-containing esterified carboxy-containing interpolymers and to lubricating compositions containing them. More particularly, this invention relates to nitrogen-containing esterified interpolymers derived from low molecular weight olefin or vinyl aromatic compounds and alpha, beta-unsaturated acylating agent, such interpolymers being esterified with aliphatic alcohols and partially neutralized with amino compounds having an average of from about 1 to about 1.1 primary or secondary amino groups. The resulting compositions are particularly useful as viscosity improvers having improved oxidative stability.
The viscosity of oils of lubricating viscosity is generally dependent upon temperature. As the temperature of the oil is increased, the viscosity usually decreases, and as the temperature is reduced, the viscosity usually increases.
The function of a viscosity improver is to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature. The fluidity characteristics of the oil are improved since the oil maintains a more consistent viscosity over a wider range of temperatures.
Viscosity improvers are usually polymeric materials and are often referred to as viscosity index improvers and sometimes as viscosity modifiers.
Ester group containing polymers are well-known additives for improving the fluidity characteristic of lubricating oils. Polyacrylate, particularly polymethacrylate ester polymers, and esterified carboxy-containing interpolymers are well-known and are widely used for this purpose.
Dispersants are also well-known in the lubricating art. Dispersants are employed in lubricants to keep impurities, particularly those formed during operation of machinery, in suspension rather than allowing them to deposit on the surfaces of parts contacted by the lubricant.
Multifunctional additives that provide both viscosity improving properties and dispersant properties are likewise known in the art. Such products are described in numerous publications including Dieter Klamann, xe2x80x9cLubricants and Related Productsxe2x80x9d, Verlag Chemie Gmbh (1984), pp 185-193; C. V. Smalheer and R. K. Smith xe2x80x9cLubricant Additivesxe2x80x9d, Lezius-Hiles Co. (1967); M. W. Ranney, xe2x80x9cLubricant Additivesxe2x80x9d, Noyes Data Corp. (1973), pp 92-145, M. W. Ranney, xe2x80x9cLubricant Additives, Recent Developmentsxe2x80x9d, Noyes Data Corp. (1978), pp 139-164; and M. W. Ranney, xe2x80x9cSynthetic Oils and Additives for Lubricantsxe2x80x9d, Noyes Data Corp. (1980), pp 96-166. Each of these publications is hereby expressly incorporated herein by reference.
It is also known to improve antioxidant properties of organic compositions such as lubricants and fuel by adding thereto antioxidant compounds such as hindered phenols, sulfur compounds, certain aromatic amines and the like.
It is desirable that the viscosity improver or dispersant viscosity improver not adversely affect the low-temperature viscosity of the lubricant containing same. Frequently, while many viscosity improvers or dispersant viscosity improvers enhance the high temperature viscosity characteristics of lubricating oil, the low temperature properties of the treated lubricant become worse.
Lubricating oils are frequently used in environments that promote oxidation, so it is desirable to manufacture products for use in lubricating oil compositions that do not undergo detrimental degradation under prolonged operating conditions in severe environments.
One of the major requirements for automatic transmission fluids has been improved low temperature performance, the current requirement approximating a maximum Brookfield viscosity of 20,000 centipoise, and more stringent future requirements as low as 10,000 centipoise at xe2x88x9240xc2x0 C. The viscosity modifier may comprise a significant proportion of the total additive system employed in an automatic transmission fluid and can have a major impact on the low temperature performance. Low temperature performance characteristics are also desirable in other applications such as in gear lubricants. The copolymers of this invention are also useful in many other lubricating oil compositions including, but not limited to engine oils, hydraulic oils, industrial oils, etc.
It is desirable, and a primary object of this invention, to provide compositions that can successfully resist oxidation under use in severe environments.
Another important object is to provide compositions that reduce the extent of loss of viscosity at high temperatures while not adversely increasing the low temperature viscosity of lubricating oil compositions.
Another object is to provide novel additive concentrates containing multi-purpose lubricant additives.
A more specific object is to provide multi-purpose additives directed to improving the viscosity and dispersant properties of a lubricating composition.
Yet another object is to provide lubricants having improved dispersant and viscosity properties.
A further object is to provide lubricants having improved oxidation properties.
Another object is to provide additive concentrates for lubricants, which additive concentrates contain esterified interpolymers that are resistant to shearing.
Other objects will in part be obvious in view of this disclosure and will in part appear hereinafter.
Various pour point depressants, additives which reduce the temperature at which oil will flow freely, have been developed and those to reach the commercial market have primarily been organic polymers, although some monomeric substances such as tetra (long chain alkyl) silicates, phenyl tristearyloxy-silane, and pentaerythritol tetrastearate have been shown to be effective. Presently available commercial pour point depressants are believed to be represented by the following types of polymeric materials: polymethacrylates, for example, copolymers of various chain length alkyl methacrylates (see, for example, U.S. Pat. No. 2,655,479); polyacrylamides (see, for example, U.S. Pat. No. 2,387,501); Friedel-Crafts condensation products of chlorinated paraffin wax with naphthalene (see, for example, U.S. Pat. No. 1,815,022 and 2,015,748); Friedel-Crafts condensation products of chlorinated paraffin wax with phenol (see, for example, U.S. Pat. No. 2,191,498); and vinyl carboxylate, such as dialkyl fumarate copolymers (see, for example, U.S. Pat. Nos. 2,666,746; 2,721,877 and 2,721,878).
Esters of maleic anhydride/alpha-olefin copolymers have been suggested as pour point depressants. For example, U.S. Pat. No. 2,977,334 describes the use of copolymers of maleic anhydride and ethylene which are esterified with low or high molecular weight alcohols and/or amidized with an amine. These resins are described as being useful as pour point modifiers, gelling agents, thickeners, viscosity improvers, etc., for mineral and synthetic oils including functional fluids and lubricating oils. U.S. Pat. No. 2,992,987 describes a class of lubricant additives useful as pour point depressants which are ethylene-maleic anhydride copolymers esterified to 80% or more, preferably 90-100%, with a mixture of straight-chain saturated hydrocarbon alcohols having from 8 to 24 carbon atoms. The unesterified carboxylic groups can be left unreacted or can be reacted with such materials as ethylene or propylene oxide alcohol esters, or lower-dialkylamino-lower-alkylene-amines. U.S. Pat. No. 3,329,658 and 3,449,250 describe copolymers of maleic anhydride and alpha-olefins such as ethylene, propylene, isobutylene or vinyl aromatic compounds such as styrene as being useful dispersancy and detergency additives for oils, as well as pour point depressants and viscosity index improvers. The copolymer is esterified to about 30 to about 95% with aliphatic alcohols or mixtures of alcohols having from 10 to 20 carbon atoms, and the remaining carboxyl groups are reacted with an amine of the following formula: 
where R1 and R2 are selected from the group consisting of aliphatic hydrocarbon radicals having from 1 to 4 carbon atoms and the cyclohexyl radical, R3 is an aliphatic hydrocarbon radical having from 2 to 4 carbon atoms, and R4 is selected from the group consisting of hydrogen and aliphatic hydrocarbon radicals having from 1 to 4 carbon atoms.
U.S. Pat. No. 3,702,300 and 3,933,761 describe carboxy-containing interpolymers in which some of the carboxy radicals are esterified and the remaining carboxy radicals are neutralized by reaction with a polyamino compound having one primary or secondary amino group and at least one mono-functional amino group, and indicate that such interpolymers are useful as viscosity index improving and anti-sludge agents in lubricating compositions and fuels. The patentee indicates that it is critical that the mixed esters described in these patents include both relatively high molecular weight carboxylic ester groups having at least eight aliphatic carbon atoms in the ester radical and relatively low molecular weight carboxylic ester groups having no more than seven aliphatic carbon atoms in the ester radical.
U.S. Pat. No. 4,604,221 relates to interpolymers similar to those described in the aforementioned ""300 and ""761 patents, except the ester groups contain at least 8 carbon atoms in the ester radical.
U.S. Pat. No. 5,124,059 describes esters of similar interpolymers characterized by the presence within its polymeric structure of the following groups which are derived from carboxy groups of said interpolymer:
(A) at least one carboxylic ester group having at least 8 aliphatic carbon atoms in the ester group;
(B) at least one carboxylic ester group having an ester group of the formula 
wherein R is a hydrocarbyl group of about 1 to about 50 carbon atoms, Rxe2x80x2 is a hydrocarbyl group of about 1 to about 50 carbon atoms, y is a number in the range of zero to about 50 and z is a number in the range of zero to about 50 with the proviso that both y and z cannot be zero; and optionally
(C) at least one carboxylic ester group having no more than 7 aliphatic carbon atoms in the ester group.
U.S. Pat. No. 3,956,149 issued to Coleman relates to a lubricant or fuel composition containing a nitrogen-containing ester of a carboxy-containing interpolymer.
U.S. Pat. No. 3,959,159 issued to Coleman relates to lubricating compositions containing a nitrogen-containing mixed ester of a carboxy-containing interpolymer.
U.S. Pat. No. 4,284,414 issued to Bryant relates to a crude oil composition containing mixed alkyl esters of a carboxy-containing interpolymer.
U.S. Pat. No. 4,180,637 issued to Evani et al. relates to a process for preparing a low molecular weight carboxy-containing copolymer.
U.S. Pat. No. 4,200,720 issued to Evani et al. relates to a process for preparing a low molecular weight carboxy-containing interpolymer.
U.S. Pat. No. 3,085,994 issued to Muskat relates to a carboxy-containing interpolymer.
U.S. Pat. No. 3,388,106 issued to Muskat relates to a process for making a carboxy-containing interpolymer.
U.S. Pat. No. 3,392,155 issued to Muskat relates to a polyoxy alkylene glycol ester of a carboxy-containing interpolymer.
U.S. Pat. No. 5,157,088 relates to nitrogen-containing, esters of carboxy-containing interpolymers having relatively low inherent viscosity.
EP 0 848 053 A1 describes mixtures of estenfied carboxy-containing interpolymers and additive concentrates and lubricating oil compositions containing same. Residual acidity of the esterified interpolymers may be neutralized by reaction with an amine.
U.S. Pat. No. 4,088,589 relates to lubricating oils blended from petroleum distillates and, if desired, a bright stock containing waxy or wax-like components and modified by the presence of copolymeric ethylene-higher alpha-olefins viscosity index improving agents, having their low temperature performance improved when said copolymer contains a minor weight proportion of ethylene by the addition of from 0.15 to 1%, based on the total weight of said lubricating oil composition of a combination of pour point depressants comprising: (a) from about 0.05 to about 0.75 wt. % of an oil-soluble condensation product of a chlorinated wax of from 10 to 50 carbon atoms and a mono- or dinuclear aromatic compound; and (b) from 0.05 to 0.75 wt. % of an oil soluble polymer of C10-8 alkyl acrylate and/or an interpolymer of a vinyl alcohol ester of a C2 to C18 alkanoic acid and di-(C4-C18 alkyl) fumarate.
The Society of Automotive Engineers (SAE) has issued a standard, J-300 (December 1995), which defines limits for classification of engine lubricating oils in rheological terms. This standard contains limits for various engine oil viscosity grades. Also included in the standard are discussions of low temperature and of high temperature test methods.
A review of developments in low temperature performance is presented by Schaub, xe2x80x9cA History of ASTM Accomplishments in Low Temperature Engine Oil Rheologyxe2x80x9d in xe2x80x9cLow Temperature Lubricant Rheology Measurement and Relevance to Engine Operationxe2x80x9d, R. B. Rhodes, ed., ASTM, Philadelphia, Pa. (1992), pp 1-19.
Nitrogen-containing esters of carboxy-containing interpolymers having superior oxidation stability and low temperature characteristics over other, similar viscosity modifiers are provided in accordance with the present invention. When added to lubricant compositions, these esters provide such lubricant compositions with surprisingly superior oxidative stability, as well as low temperature properties and other desirable properties including dispersancy and viscosity index improvement. These nitrogen-containing esters also enhance the dispersion of other additives as well as contaminants (e.g., dirt, water, metallic particles, etc.) in the lubricating compositions to which they are added.
Broadly stated, the present invention provides nitrogen-containing esters derived from a carboxy-containing interpolymer having a reduced specific viscosity (RSV) of from about 0.05 to about 2, said interpolymer being derived from at least two monomers, (i) one of said monomers being at least one of an aliphatic olefin containing from 2 to about 30 carbon atoms and a vinyl aromatic monomer and (ii) the other of said monomers being at least one xcex1,xcex2-unsaturated acylating agent, said nitrogen containing ester being characterized by the presence within its polymeric structure of each of the following groups which are derived from the carboxy groups of said interpolymer:
(A) from about 20 to about 70 mole % based on moles of carboxyl groups in said interpolymer, of ester groups containing from about 13 to about 19 carbon atoms,
(B) from about 80 to about 30 mole %, based on moles of carboxyl groups in said interpolymer, of ester groups containing from about 8 to about 12 carbon atoms, optionally,
(C) up to about 20 mole %, based on moles of carboxyl groups in said interpolymer, of ester groups containing from 2 to 7 carbon atoms, wherein from about 93 to about 97% of the carboxy groups derived from the carboxy-containing interpolymer are ester groups, the balance of the carboxy groups comprising residual carboxylic acid or anhydride groups which are then reacted with at least one amino compound having an average of from 1 to about 1.1 primary or secondary amino groups, in amounts to convert from about 5 up to less than 50% of the carboxylic acid or anhydride groups to
(D) carbonyl-amino groups, with the unreacted carboxylic acid or anhydride groups remaining as
(E) residual carboxylic acid or anhydride groups.
Additive concentrates and lubricant compositions comprising the foregoing nitrogen-containing esterified interpolymers are also provided in accordance with the present invention.
According to the present invention compositions suitable for use as a dispersant-viscosity improver for preparing lubricating oil compositions comprise esterified interpolymers derived from a mixture of monomers as set forth in greater detail hereinabove and hereinbelow. The invention also contemplates additive concentrates and lubricating oil compositions.
As used herein, the terms xe2x80x9chydrocarbonxe2x80x9d, xe2x80x9chydrocarbylxe2x80x9d or xe2x80x9chydrocarbon basedxe2x80x9d mean that the group being described has predominantly hydrocarbon character within the context of this invention. These include groups that are purely hydrocarbon in nature, that is, they contain only carbon and hydrogen. They may also include groups containing substituents or atoms which do not alter the predominantly hydrocarbon character of the group. Such substituents may include halo-, alkoxy-, nitro-, etc. These groups also may contain hetero atoms. Suitable hetero atoms will be apparent to those skilled in the art and include, for example, sulfur, nitrogen and oxygen. Therefore, while remaining predominantly hydrocarbon in character within the context of this invention, these groups may contain atoms other than carbon present in a chain or ring otherwise composed of carbon atoms.
In general, no more than about three non-hydrocarbon substituents or hetero atoms, and preferably no more than one, will be present for every 10 carbon atoms in the hydrocarbon or hydrocarbon based groups. Most preferably, the groups are purely hydrocarbon in nature, that is, they are essentially free of atoms other than carbon and hydrogen.
Throughout the specification and claims the expression oil soluble or dispersible is used. By oil soluble or dispersible is meant that an amount needed to provide the desired level of activity or performance can be incorporated by being dissolved, dispersed or suspended in an oil of lubricating viscosity. Usually, this means that at least about 0.001% by weight of the material can be incorporated in a lubricating oil composition. For a further discussion of the terms oil soluble and dispersible, particularly xe2x80x9cstably dispersiblexe2x80x9d, see U.S. Pat. No. 4,320,019 which is expressly incorporated herein by reference for relevant teachings in this regard.
As used in the specification and in the appended claims, the singular forms xe2x80x9caxe2x80x9d, xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d include plural unless the context clearly dictates otherwise. Thus, for example, reference to a polymer includes mixtures of polymers, reference to an acylating agent includes mixtures of acylating agents, etc.
In the context of this invention the term xe2x80x9cinterpolymerxe2x80x9d means a polymer derived from two or more different monomers.
As used in the specification and claims, the term carboxy-containing refers to polymers which are prepared using a carboxy-containing monomer. The carboxy-containing monomer is polymerized with other monomers to form the carboxy-containing interpolymer. Since the carboxy-containing monomer is incorporated into the polymer backbone, the carboxy groups extend from the polymer backbone, e.g., the carboxy groups are directly attached to the polymer backbone.
As described above, the invention relates to nitrogen containing esters derived from carboxy-containing interpolymers.
In reference to the size of the ester groups, it is pointed out that an ester group is represented by the formula
xe2x80x94C(O)(OR)
and that the number of carbon atoms in an ester group is thus the combined total of the carbon atom of the carbonyl group and the carbon atoms of the (OR) group. Thus, methyl methacrylate contains two carbon atoms in the ester group. A butyl ester contains five carbon atoms in the ester group.
In one embodiment, the present invention relates to a mixture of organic diluent and esterified interpolymers. Certain diluents, as will be discussed in greater detail hereinbelow, provide improved low temperature properties and further enhanced resistance to oxidation.
One optional element of the present invention is the presence of up to about 20 mole %, based on moles of carboxyl group in the interpolymer, of ester groups containing from 2 to 7 carbon atoms.
Another element of the present invention is the presence of amino groups derived from amino compounds, and particularly amino compounds having an average of from 1 to about 1.1 primary or secondary amino groups. In one embodiment the amino compound is a polyamino compound having at least one mono-functional amino group. Such amino groups, when present in the esters of the present invention in the proportion stated above, enhance the dispersant properties of such esters in lubricant compositions and dispersibility of additives for lubricant compositions.
An essential feature of the instant invention is the extent of esterification and the extent of neutralization of the unesterified carboxy groups of the carboxy-containing interpolymer through the conversion thereof to amino-containing groups. It should be noted that the linkage described as the carbonyl-amino group may be salt, imide, amide, amidine and inasmuch as any such linkage is contemplated within the present invention, the term xe2x80x9ccarbonyl aminoxe2x80x9d is thought to be a convenient, generic expression useful for the purpose of defining the inventive concept. In a particularly advantageous embodiment of the invention such linkage is amide or imide, predominantly imide.
We have found that both the amount of amine used, as well as the way in which it is bound into the polymer ester is of extreme importance, and can have a significant impact on the oxidative stability of the final products. If the amino compounds are firmly bound to the polymer by stable amide or imide links, the oxidation stability will be enhanced. But if the stable amide and/or imide links are not formed, much of the amine will be attached in the form of carboxylic acid salts which can be susceptible to attack by oxygen and peroxides to a surprising extent. We have also found that using a calculated stoichiometric amount of amine, as would be the expected and common practice, does not necessarily assure that more of the desired stable amide and/or imide bonds will be formed. Surprisingly, we have found that, by using less that stoichiometric amounts of amine, although the total amount of amine incorporated into the composition is lower, the relative amount of stable amide and/or imide bonds formed, compared to unstable salts is higher, and oxidative stability is enhanced.
Still another important element of the present invention is the molecular weight of the carboxy-containing interpolymer before esterification. Whenever reference is made in this application to RSV or reduced specific viscosity, the reference is to the interpolymer before it is esterified. For convenience, the molecular weight is expressed in terms of the xe2x80x9creduced specific viscosityxe2x80x9d of the interpolymer which is a widely recognized means of expressing the molecular size of a polymeric substance. As used herein, the reduced specific viscosity (abbreviated RSV) is the value obtained in accordance with the formula   RSV  =                    Relative        ⁢                  xe2x80x83                ⁢        Viscosity            -      1        Concentration  
wherein the relative viscosity is determined by measuring, by means of a dilution viscometer, the viscosity of a solution of one gram of the interpolymer in 100 ml. of acetone and the viscosity of acetone at 30 xc2x0xc2x10.02xc2x0 C. For purpose of computation by the above formula, the concentration is adjusted to 0.4 gram of the interpolymer per 100 ml. of acetone. A more detailed discussion of the reduced specific viscosity, also known as the reduced viscosity, as well as its relationship to the average molecular weight of an interpolymer, appears in Paul J. Flory, Principles of Polymer Chemistry, (1953 Edition) pages 308 et seq; Mark, Bikales, Overberger and Menges, Eds., Encyclopedia of Polymer Science and Engineering, 2nd ed., Wiley Interscience (1988), V. 14, pp 463-465; and F. W. Billmeyer, Textbook of Polymer Science, Wiley Publishing (1962), pp 79-85.
The Interpolymer
The carboxy-containing interpolymers useful in preparing the esters useful in the invention are copolymers, terpolymers, and other interpolymers of at least two monomers, (i) one of said monomers being at least one of an aliphatic olefin containing from 2 to about 30 carbon atoms and a vinyl aromatic monomer and (ii) the other of said monomers being at least one alpha, beta-unsaturated acylating agent, typically a carboxylic acid or derivative thereof. Derivatives of the carboxylic acid are those which are polymerizable with (i) the olefin or the vinyl aromatic monomers, and as such may be the esters, especially lower alkyl esters, e.g., those containing from 2 to 7 carbon atoms in the ester alkyl group, especially 2 carbon atoms, halides and anhydrides of the acids. The molar ratio of (i) to (ii) ranges from about 1:2 to about 3:1, preferably about 1:1. The carboxy-containing interpolymer is prepared by polymerizing the olefin or vinyl aromatic monomer with the alpha, beta-unsaturated carboxylic acid or derivative thereof.
Mixtures of two or more compatible (i.e., nonreactive to one another) interpolymers which are separately prepared are contemplated herein for use in the esterification reaction, if each has a RSV as described herein. Thus, as used herein, and in the appended claims, the terminology xe2x80x9cinterpolymerxe2x80x9d refers to either one separately prepared interpolymer or a mixture of two or more of such interpolymers. A separately prepared interpolymer is one in which the reactants and/or reaction conditions are different from the preparation of another interpolymer.
Interpolymers having RSV from about 0.05 to about 2 are contemplated in the present invention. Preferred interpolymers are those having RSV of from about 0.05, frequently from about 0.08, often from about 0.12 or about 0.2 to about 0.8 frequently to about 0.35, often to about 0.25. In another embodiment, the RSV ranges from about 0.05, often from about 0.08, to about 0.45; in still another embodiment, from about 0.08 to about 0.35. Interpolymers having RSV of from about 0.08 to about 0.25 or from about 0.10 to about 0.2 are particularly useful.
Aliphatic Olefins
Suitable aliphatic olefin monomers that are useful in the preparation of the interpolymers of the invention are mono-olefins of about 2 to about 30 carbon atoms. Included in this group are internal olefins (i.e., wherein the olefinic unsaturation is not in the xe2x80x9c1xe2x80x9d or alpha position) and mono-1-olefins or alpha-olefins. Alpha olefins are preferred. Exemplary olefins include ethylene, propylene, 1-butene, isobutene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 1-heptene, 1-octene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 1-heneicosene, 1-docosene, 1-tetracosene, 1-pentacosene, 1-hexacosene, 1-octacosene, 1-nonacosene, etc. Commercially available alpha-olefin can also be used. Exemplary alpha-olefin mixtures include C15-18 alpha-olefins, C12-16 alpha-olefins, C14-16 alpha-olefins, C14-18 alpha-olefins, C16-18 alpha-olefins, C16-20 alpha-olefins, C22-28 alpha-olefins, etc. Additionally, C30+alpha-olefin fractions such as those available from Conoco, Inc. can be used. Preferred olefin monomers include ethylene, propylene and 1-butene.
The mono-olefins can be derived from the cracking of paraffin wax. The wax cracking process yields both even and odd number C6-20 liquid olefins of which 85 to 90% are straight chain 1-olefins. The balance of the cracked wax olefins is made up of internal olefins, branched olefins, diolefins, aromatics and impurities. Distillation of the C6-20 liquid olefins obtained from the wax cracking process yields fractions (e.g., C15-18 alpha-olefins) which are useful in preparing the interpolymers of this invention.
Other mono-olefins can be derived from the ethylene chain growth process. This process yields even numbered straight chain 1-olefins from a controlled Ziegler polymerization.
Other methods for preparing the mono-olefins of this invention include chlorination-dehydrochlorination of paraffin and catalytic dehydrogenation of paraffins.
The above procedures for the preparation of mono-olefins are well known to hose of ordinary skill in the art and are described in detail under the heading xe2x80x9cOlefinsxe2x80x9d in the Encyclopedia of Chemical Technology, Second Edition, Kirk and Othmer, Supplement, pages 632-657, Interscience Publishers, Div. of John Wiley and Son, 1971, which is hereby incorporated by reference for its relevant disclosures pertaining to methods for preparing mono-olefins.
Vinyl Aromatic Monomers
Suitable vinyl aromatic monomers which can be polymerized with the alpha, beta-unsaturated acylating agents include styrene and the substituted styrenes. Other vinyl aromatic monomers such as the vinyl anthracenes and vinyl naphthalenes can also be used. Substituted styrenes include styrenes that have halo-, alkoxy-, carboxy-, hydroxy-, sulfonyl-, hydrocarbyl- wherein the hydrocarbyl group has from 1 to about 12 carbon atoms and other substituents. Exemplary of the hydrocarbyl-substituted styrenes are alpha-methylstyrene, para-tert-butylstyrene, alpha-ethylstyrene, and para-lower alkoxy styrene. Mixtures of two or more vinyl aromatic monomers can be used. Styrene and alkylstyrenes are preferred.
Alpha, Beta-Unsaturated Acylating Agent
Suitable alpha, beta-unsaturated acylating agents useful in the preparation of the interpolymers are represented by carboxylic acids, anhydrides, halides, or lower alkyl esters thereof. These include mono-carboxylic acids (e.g., acrylic acid, methacrylic acid, etc. and esters, preferably lower alkyl esters thereof, as well as dicarboxylic acids, anhydrides and esters, preferably lower alkyl esters thereof wherein a carbon-to-carbon double bond is in an alpha, beta-position to at least one of the carboxy functions (e.g., itaconic acid, anhydride or esters thereof, xcex1-methylene glutaric acid or esters thereof,) and preferably in an alpha, beta-position to both of the carboxy functions of the alpha, beta-dicarboxylic acid, anhydride or the ester thereof (e.g., maleic acid or anhydride, fumaric acid, or ester, preferably lower alkyl, i.e., those containing no more than 7 carbon atoms, esters thereof). Normally, the carboxy functions of these compounds will be separated by up to about 4 carbon atoms, preferably about 2 carbon atoms.
A class of preferred alpha,beta-unsaturated dicarboxylic acid, anhydrides or esters, preferably the lower alkyl esters thereof, includes those compounds corresponding to the formulae: 
(including the geometric isomers thereof, i.e., cis and trans) wherein each R is independently hydrogen; halogen (e.g., chloro, bromo, or iodo); hydrocarbyl or halogen-substituted hydrocarbyl of up to about 8 carbon atoms, preferably alkyl, alkaryl or aryl; (preferably, at least one R is hydrogen, more preferably, both R are hydrogen); and each Rxe2x80x2 is independently hydrogen or hydrocarbyl, preferably lower alkyl of up to about 7 carbon atoms (e.g., methyl, ethyl, butyl or heptyl). These alpha, beta-unsaturated dicarboxylic acids, anhydrides or alkyl esters thereof contain a total carbon content of up to about 25 carbon atoms, normally up to about 15 carbon atoms. Examples include maleic acid or anhydride; benzyl maleic anhydride; chloro maleic anhydride; heptyl maleate; itaconic acid or anhydride; citraconic acid or anhydride, ethyl fumarate; fumaric acid, mesaconic acid; ethyl isopropyl maleate; isopropyl fumarate; hexyl methyl maleate; phenyl maleic anhydride and the like. These and other alpha, beta-unsaturated dicarboxylic compounds are well known in the art. Maleic anhydride, maleic acid and fumaric acid and the lower alkyl esters thereof are preferred. Interpolymers derived from the mixtures of two or more of any of these can also be used.
Alternatively, the (ORxe2x80x2) group in the above formula may contain more than 7 arbon atoms, being derived from a mixture of alcohols, some containing over 7 arbon atoms, and in such instances, the ester group may remain attached to the carboxy group during and after formation of the interpolymer. This procedure provides a method of introducing the desirable ester groups initially, and eliminates the need to introduce the ester groups in a separate subsequent step.
In another preferred embodiment, the alpha, beta-unsaturated agent comprises a mixture of two or more components. Thus, interpolymers prepared from reaction mixtures wherein (ii) comprises 2 or more, usually up to 4, preferably 2, different alpha-beta unsaturated acylating agents are contemplated. A non-limiting example might be a mixture of maleic acid or anhydride with esters of acrylic acids. Other mixtures are contemplated.
When (ii) comprises a mixture of monomeric components, they may be present in any amounts relative to one another. However, it is preferred that one of the components is present in a major amount, i.e., more than 50 mole % of the mixture. In an especially preferred embodiment, the total amount of additional components is present in amounts ranging from. about 0.005 to about 0.3 moles, per mole of major component, more often from about 0.01 to about 0.15 moles, preferably from about 0.03 to about 0.1 moles minor component per mole of major component.
Examples of preferred mixtures of acylating agents are maleic acid or anhydride with esters of acrylic acids, especially esters of methacrylic acid. Preferred esters are lower alkyl esters. An especially preferred mixture of acylating agents is one containing maleic anhydride and methacrylic acid or lower alkyl esters of methacrylic acid. Especially preferred is a mixture of maleic anhydride and methyl or ethyl, preferably methyl, methacrylate.
Particularly preferred esters of this invention are those of interpolymers made by reacting maleic acid, or anhydride or the lower esters thereof with styrene. Of these particularly preferred interpolymers, those which are made of maleic anhydride and styrene and have a RSV in the range of about 0.05 to about 0.8 preferably to about 0.5, often to about 0.35, preferably from about 0.08 to about 0.25, are especially useful. Of these latter preferred interpolymers, copolymers of maleic anhydride and styrene having a molar ratio of the maleic anhydride to styrene of bout 1:1 are especially preferred. They can be prepared according to methods known in the art, as for example, free radical initiated (e.g., by benzoyl peroxide) solution polymerization. Suitable interpolymerization techniques are well known in the art and are described in numerous U.S. Patents including U.S. Pat. Nos. 2,938,016; 2,980,653; 3,085,994; 3,342,787; 3,418,292; 3,451,979; 3,536,461; 3,558,570; 3,702,300; 3,723,375; 3,933,761; 4,284,414, and 4,604,221. These patents are incorporated herein by reference for their teaching of the preparation of suitable interpolymers, especially maleic anhydride and styrene containing interpolymers. Other preparative techniques are known in the art.
The carboxy-containing interpolymers may also be prepared using one or more additional interpolymerizable comonomers. The additional comonomer is present in relatively minor proportions. Generally, the total amount is less than about 0.3 mole, usually less than about 0.15 mole of additional comonomers for each mole of either the olefin or the alpha, beta-unsaturated carboxylic acylating agent. Examples of additional comonomers include acrylamides, acrylonitrile, vinyl pyrrolidinone, vinyl pyridine, vinyl ethers, and vinyl carboxylates. In one embodiment, the additional comonomers are vinyl ethers or vinyl carboxylates.
Vinyl ethers are represented by the formula R1xe2x80x94CHxe2x95x90CHxe2x80x94OR2 wherein each R1 is hydrogen or a hydrocarbyl group having 1 to about 30, or to about 24, or to about 12 carbon atoms and R2 is a hydrocarbyl group having 1 to about 30 carbon atoms, or to about 24, or to about 12. Examples of vinyl ethers include methyl vinyl ether, propyl vinyl ether, 2-ethylhexyl vinyl ether and the like.
The vinyl ester of a carboxylic acid may be represented by the formula R3CHxe2x95x90CHxe2x80x94O(O)CR4 wherein R3 is a hydrogen or hydrocarbyl group having from 1 to about 30, or to 12 carbon atoms, or just hydrogen, and R4 is a hydrocarbyl group having 1 to about 30, or to about 12, or to about 8. Examples of vinyl esters include vinyl acetate, vinyl 2-ethylhexanoate, vinyl butanoate, vinyl crotonate.
The molecular weight (i.e., RSV) of such interpolymers can be adjusted to the range required in this invention, if necessary, according to conventional techniques, e.g., control of the reaction conditions.
Preferred interpolymers are prepared from a vinyl aromatic monomer and aliphatic carboxylic acids or anhydrides and esters thereof.
Preferably, the vinyl aromatic monomer is styrene or a substituted styrene (either ring substituted or substituted on the aliphatic xe2x80x94Cxe2x95x90C group), most preferably, styrene.
Preferably, the aliphatic carboxylic acid or anhydride and esters thereof is at least one member selected from the group consisting of maleic acid or anhydride, itaconic acid or anhydride, fumaric acid, xcex1-methylene glutaric acid, acrylic acid, methacrylic acid or an ester thereof or half acid-esters of the dibasic compounds.
In one preferred embodiment the interpolymer is derived from styrene and maleic anhydride. In another preferred embodiment the interpolymer is derived from styrene, maleic anhydride and methacrylic acid or an ester thereof.
In the latter preferred embodiment, the mole ratio of styrene:maleic anhydride:methacrylic acid or ester thereof ranges from about (1-3):(2-1):(0.01-0.3), preferably from about (1-2):(1.5-1):(0.01-0.03), more preferably from 1:1:(0.03-0.08), most preferably from 1: 1:0.05.
Esterification
Esterification (or transesterification, when the interpolymer contains ester groups) of the interpolymers can be accomplished by heating any of the interpolymers (having the requisite RSV) and the desired alcohol(s) and alkoxylate(s) under conditions typical for effecting esterification. Such conditions include, for example, a temperature of at least about 80xc2x0 C., but more preferably up to about 150xc2x0 C. or even more, provided that the temperature is maintained below the lowest decomposition temperature of any component of the reaction mixture or products thereof. Water or lower alcohol is normally removed as the esterification proceeds. These conditions may optionally include the use of a substantially inert, normally liquid, organic solvent or diluent such as mineral oil, toluene, benzene, xylene or the like and an esterification catalyst such as toluene sulfonic acid, sulfuric acid, aluminum chloride, boron trifluoride-triethylamine, methane sulfonic acid, hydrochloric acid, ammonium sulfate, phosphoric acid, sodium methoxide and the like. These conditions and variations thereof are well known in the art.
At least about 93%, preferably at least about 95% up to about 97% of the carboxy functions of the interpolymer are converted to ester groups. An excess of alcohols and alkoxylates over the stoichiometric requirement for complete esterification of the carboxy functions may be used in the esterification process provided the ester content remains within the 93-97% range. While excess of alcohols and alkoxylates or unreacted alcohols and alkoxylates need not be removed as such alcohols and alkoxylates can serve, for example, as diluent or solvent in the use of the esters, and similarly, optional reaction media, e.g., toluene, need not be removed as they can similarly serve as diluent or solvent in the use of the esters, it is generally preferred that unreacted alcohols, alkoxylates and diluents are removed by techniques such as distillation, etc., that are well-known in the art.
As noted above, the compositions of this invention contain ester groups. From about 20 to about 70 mole % based on the total number of moles of carboxyl groups in the interpolymer contain ester groups having from about 13 to about 19 carbon atoms and from about 80 to about 30 mole % based on the total number of moles of carboxyl groups in the interpolymer contain ester groups having from about 8 to about 12 carbon atoms. Preferably, the ester contains at least about 45 mole %, based on moles of carboxyl groups in said interpolymer, of ester groups containing from about 8 to about 12 carbon atoms. In an optional embodiment, the esterified interpolymer has up to about 20 mole % based on the total number of moles of carboxyl groups in the interpolymer of ester groups having from 2 to 7 carbon atoms. Preferably, the compositions are substantially free of ester groups containing from 3 to 7 carbon atoms. The ester groups are usually formed by reacting the carboxy-containing interpolymer with alcohols although frequently, especially for lower alkyl esters, the ester group may be incorporated from one of the monomers used to prepare the interpolymer. Examples of useful alcohol reactants include heptanol, octanol, 2-ethylhexanol, decanol, dodecanol, tridecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, etc.
One class of alcohols includes commercially available mixtures of alcohols. These include oxoalcohols which may comprise, for example, various mixtures of alcohols having from about 8-24 carbon atoms. Of the various commercial alcohols useful in this invention, one contains from about 8 to about 10 carbon atoms, and another from about 12 to about 18 aliphatic carbon atoms. The alcohols may comprise, for example, octyl alcohol, decyl alcohol, dodecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, octadecyl alcohol, etc. Several suitable sources of these alcohol mixtures are the technical grade alcohols sold under the name NEODOL(copyright) alcohols (Shell Oil Company, Houston, Tex.) and under the name ALFOL(copyright) alcohols (Vista Chemical, Westlake, La.), and fatty alcohols derived from animal and vegetable fats and sold commercially by, for example, Henkel, Condea, and Emory.
Tertiary alkanolamines, i.e., N,N-di-(lower alkyl)amino alkanolamines, may be used to prepare the esterified interpolymers. Examples include N,N-dimethylethanolamine, N,N-diethylethanolamine, and 5-diethylamino-2-pentanol.
The esterified interpolymers may be mixed esters derived from a combination of alcohols including alcohols containing at least 7, often at least 12 carbon atoms (relatively high molecular weight alcohols) and alcohols containing less than 7 carbon atoms (relatively low molecular weight alcohols). Alcohols containing less than 7 carbon atoms include methanol, ethanol, propanol, butanol, pentanol and hexanol, including isomers thereof.
Mixed esters of the carboxy-containing interpolymer are most conveniently prepared by first esterifying the carboxy-containing interpolymer with the relatively high molecular weight alcohols then with the relatively low molecular weight alcohol in appropriate amounts, to convert at least about 93% up to about 97% of the carboxy groups of the interpolymer to ester groups. Nitrogen-containing esters are prepared by neutralizing from about 5% up to less than 50% of the remaining carboxy groups with ammonia, an amine, or a hydrazine such as those described below to obtain nitrogen-containing esters.
When utilizing a combination of high molecular weight and low molecular weight alcohols, the esterification may be carnied out, for example, by initially esterifying the carboxy radicals with the higher molecular weight alcohols and then subsequently esterifying the partially-esterified carboxy-containing interpolymer with a low molecular weight, e.g., 1-6 carbon atoms, alcohol, to obtain a carboxy interpolymer having at least about 80% of the ester groups high molecular weight esters and the balance of the ester groups being low molecular weight esters. For example, esterification with a combination of high and low molecular weight alcohols may be accomplished in sequence, first carrying out the esterification with the high molecular weight alcohol then esterifying the remaining carboxylic groups with the low molecular weight alcohol, to attain the desired degree of esterification.
Alternatively, the carboxylic groups of the interpolymer may be simultaneously esterified with a mixture of the alcohols to obtain an esterified carboxy-containing interpolymer wherein at least about 80 mole percent of the ester groups have been obtained from high molecular weight alcohols and the balance of the ester groups being obtained from low molecular weight alcohols.
The Amino Compound
The carboxy-containing interpolymers contains a carbonyl-amino group. The carbonyl-amino groups include amides, imides, amidines, ammonium salts, amidic acid salts or mixtures thereof. Thus, use of the expressions xe2x80x9cneutralize, neutralizing, etcxe2x80x9d are not to be limiting to salt formation but refer to reaction of an amino compound with a carboxylic acid or functional derivative thereof. A carbonyl-amino group is derived from unesterified carboxylic acid or anhydride groups of the esterified interpolymer and an amino compound.
Amino compounds include ammonia and amines. Amines which are used to form carbonyl-amino groups may be mono- or polyamines provided that the average number of primary and secondary amino nitrogens is from 1 up to about 1.1. To illustrate, the amine may be a monoamine containing one primary or secondary amino group alone or in admixture with a polyamine having 2 or more primary and secondary amino nitrogens. The amino compound may be a polyamine, wherein one amino group is primary or secondary and one or more is tertiary. Aminopropylmorpholine and dimethylaminopropyl amine are examples. The amino compound may also be a mixture of these with one or more polyamines containing 2 or more primary or secondary amino groups, provided that the average number of primary or secondary amino groups in the mixture is no greater than about 1.1, preferably less than 1.05.
Examples of monoamines include aliphatic amines such as mono- and di-alkyl amines having alkyl groups containing from 1 to about 20 carbon atoms as well as cyclic monoamines.
In one embodiment, the amines are polyamines having an average of from 1 to about 1.1, preferably one, primary or secondary amino group, and at least one non-condensable mono-functional amino group such as a tertiary-amino group, a functionally-substituted nitrogen atom, or a nitrogen heterocyclic group derived from pyrroles, pyrrolidones, caprolactams, oxazolidones, oxazoles, thiazoles, pyrazoles, pyrazolines, imidazoles, imidazolines, thiazines, oxazines, diazines, oxacarbamyl, thiocarbamyl, uracils, hydantoins, thiohydantoins, guanidines, ureas, sulfonamides, phosphoramides, phenolthiazines, amidines, etc. In one embodiment, the carbonyl-polyamino group is derived from a morpholine. Examples of suitable morpholines include aminoethylmorpholine, aminopropylmorpholine, etc. Examples of such polyamines include dimethylamino-ethylamine, dibutylamino-ethylamine, 3-dimethylamino-1-propylamine, 4methylethylamino-1-butylamine, pyridyl-ethylamine, N-morpholinoethylamine, tetrahydropyridyl-ethylamine, bis-(dimethylamino)propylamine, bis(diethylamino)ethylamine, N,N-dimethyl-p-phenylenediamine, piperidyl-ethylamine, 1-aminoethylpyrazone, 2-amino-5-mercapto-thiadiazole, 1-(methyl-amino)pyrazoline, 1-methyl 4-aminooctyl pyrazole, 1-aminobutylimidazole, 4-aminoethylthiazole, 2-aminoethyltriazine, dimethylcarbamylpropylamine, N-methyl-N-aminopropylacetamide, N-aminoethylsuccinimide, N-methylamino-maleimide, N-aminobutylalpha-chlorosuccinimide, 3-aminoethyluracil, 2-amino-ethylpyridine, ortho-aminoethyl-N,N-dimethylbenzenesulfamide, N-aminoethyl-phenothiazine, N-aminoethylacetamidine, 1-aminophenyl-2-methyl-imidazoline, N-methyl-N-aminoethyl-S-ethyidithiocarbamate, etc. For the most part, the amines are those which contain only one primary-amino or secondary-amino group and, preferably at least one tertiary-amino group. The tertiary amino group is preferably a heterocyclic amino group. In some instances polyamines may contain up to about 6 amino groups although, in most instances, they contain one primary-amino group and either one or two tertiary-amino groups. The polyamines may be aromatic or aliphatic amines and are preferably heterocyclic amines such as aminoalkyl-substituted morpholines, piperazines, pyridines, benzopyrroles, quinolines, pyrroles, etc. They are usually amines having from 4 to about 30, or to about 12 carbon atoms. Polar substituents may likewise be present in the amines.
The carbonyl-amino groups of the carboxy-containing interpolymers also may comprise the groups derived from hydrazine and/or a hydrocarbon-substituted hydrazine including, for example, the mono-, di-, and tri-hydrocarbon-substituted hydrazines wherein the hydrocarbon substituent is either an aliphatic or aromatic substituent including, for example, alkyl-, e.g., cyclic and/or acyclic groups, aryl-, e.g., alkaryl-, aralkyl, etc. The hydrocarbon substituents, generally, contain from 1 up to about 24, often up to about 12 aliphatic carbon atoms. Preferred substituents, include for example, phenyl, alkylphenyl or an alkyl group wherein the alkyl group is either a methyl, ethyl, propyl, butyl, pentyl, octyl, cyclohexyl, decyl or dodecyl group. Other examples of the hydrocarbon groups include octadecyl, behenyl, benzyl, heptylphenyl, alpha-naphthyl, beta-naphthyl, butyl-naphthyl, oleyl, and stearyl groups. Of the various hydrocarbon-substituted hydrazines, a preferred class includes the N,N-dihydrocarbon-substituted hydrazines, e.g., the dimethyl, diethyl, diphenyl and dibutyl hydrazines.
The carboxy-containing interpolymer is characterized as containing a carbonyl-amino group. The carboxy-containing interpolymer may be esterified as described above. Following esterification of the carboxy groups of the interpolymer at least about 5 up to less than 50%, preferably from about 10% to about 40%, and more preferably from about 15% to about 35% of the residual carboxy groups remaining in the esterified interpolymer may be reacted with an amine at temperatures up to 350xc2x0 C. or higher provided that said temperature is maintained below the decomposition point of the reactants and the products obtained thereof, more often at temperatures ranging from about 80xc2x0 C., more often from about 120xc2x0 C., up to about 300xc2x0 C. Thus, for example, at least about 93 mole %, e.g., 93 to 97 mole %, of the carboxy groups of a carboxy-containing interpolymer may be esterified and then the partially esterified interpolymer is subsequently reacted with a amino compound to obtain a nitrogen-containing ester having from about 5 up to less than 50 percent of the unesterified carboxylic groups converted to carbonyl-amino groups. The amount of amino compound used is sufficient to react with up to less than 50% of the unesterified carboxy groups of the polymer.
In another embodiment, the carboxy-containing interpolymer is reacted with a relatively high molecular weight alcohol and optionally a relatively low molecular weight alcohol and an amino compound. The alcohols and amino compounds have been described above. The alcohols may be reacted with the interpolymer to form an intermediate which is subsequently reacted with the amino compound. Alternatively the alcohols and amine may be reacted with the interpolymer simultaneously. The relative proportions of the several described ranges of alkyl ester groups to the carbonyl-amino group are expressed in terms of mole percentages of (20-70): (80-30):(0-20):(0.05-3.5) respectively. The preferred ratio is (40-60):(70-45):(0-10):(0.1-3).
The amine compounds can be used alone as well as in various combinations in this final step, since the different amines can contribute different and often complementary stability characteristics to the final products. For example, amine compounds which contain sulfide and disulfide groups in their structures can interact synergistically with added phenolic and arylamine antioxidants in formulations in which they are subsequently used.
The Diluent
As noted hereinabove, the compositions of this invention may contain a diluent. Often they are prepared in the presence of the diluent. The diluent may also be added to a substantially diluent-free copolymer, usually by dissolving or dispersing a substantially diluent-free polymer in an appropriate diluent, or by adding a higher boiling point diluent to an interpolymer containing a lower boiling point diluent such as toluene and removing the lower boiling point diluent by, e.g., distillation.
A wide variety of diluents may be used, including natural oils such as mineral oils, vegetable oils and animal oils, and synthetic oils such as ester type oils, especially carboxylic esters, polyolefin oligomers, especially polyalphaolefin oligomers, or alkylated benzenes, and mixtures thereof. Selection of diluents having particular characteristics leads to enhanced performance of dispersant-viscosity improvers of this invention. Particularly valuable are oils of lubricating viscosity that display excellent viscosity characteristics at very low temperatures, for example from xe2x88x925xc2x0 C. to xe2x88x9240xc2x0 C.
Naphthenic and synthetic diluents that impart improved low temperature performance when used in conjunction with the dispersant viscosity improvers of this invention have in common very low viscosity at very low temperatures. In particular they all display Brookfield viscosities (expressed in centipoise) at xe2x88x9226xc2x0 C. ranging from about 50 to about 400, more preferably from about 80 to about 200. At xe2x88x9240xc2x0 C. useful oils have Brookfield viscosities (expressed in centipoise) ranging from about 100 to about 1500, more preferably from about 125 to about 600. Brookfield viscosities are determined employing ASTM Procedure D-2983 described in greater detail hereinafter. These particularly useful diluents display viscosities (ASTM Procedure D-445) at 40xc2x0 C. ranging from about 2.5 to about 6 centistokes and at 100xc2x0 C. ranging from about 1 to about 2.5 centistokes.
Low temperature viscosity (Brookfield Viscosity) of fluid lubricants is determined using ASTM Procedure 2983, Standard Test Method for Low Temperature Viscosity of Automotive Fluid Lubricants Measured by Brookfield Viscometer, which appears in the Annual Book of ASTM Standards, Section 5, ASTM, Philadelphia, Pa., USA. This procedure employs a Brookfield Viscometer which is described in the procedure. The device is available from Brookfield Engineering Laboratories, Stoughton, Mass., USA.
The choice of diluent also affects oxidation performance of lubricating oil compositions containing the nitrogen containing esters of this invention. While naphthenic and hydrotreated naphthenic oils can impart particularly good viscometrics at low temperature they, and compositions containing them, tend to be oxidatively unstable. In an especially preferred embodiment the diluent consists essentially of lower viscosity, highly paraffinic oils.
Hydrotreated and hydro-refined paraffinic diluent oils comprise a most desirable and cost-effective type of base fluid for the purposes of this invention. The paraffinic oils are usually essentially linear or somewhat lightly branched in 30 structure, and when processed using hydrogen contain little, if any, residual olefinic Cxe2x95x90C bonds which tend to be oxidatively susceptible. While some of the paraffinic diluent oils can contain relatively high levels (up to about 8%) of aromatic components, they are often not as oxidation-sensitive as their naphthenic oil counterparts of similar viscosity.
In general, the hydrotreated and hydro-refined types of diluent oils are preferred for the compositions of this invention, because of both their oxidation stability, and their good viscometrics at very low temperatures. Lighter viscosity hydrotreated or hydro-refined paraffinic diluents (of about 1.0-3.5 cSt kinematic viscosity at 100xc2x0 C.) are most appropriately useful with the products of this invention in automatic transmission, gear oil, and hydraulic fluid applications, while medium viscosity hydrotreated paraffinic oils (of about 4.0-7.5 cSt kinematic viscosity at 100xc2x0 C.) may also be used for application in gasoline and diesel engines.
Diluent-containing copolymers of this invention may be referred to as additive concentrates. Such additive concentrates may contain other desirable performance-improving additives which are described in greater detail hereinbelow. Additive concentrates are then added, along with other performance-improving additives, if desired, to an oil of lubricating viscosity to prepare a finished lubricant composition.
The additive concentrates preferably comprise from about 25 to about 85% by weight, preferably from 35% to about 80% by weight of the nitrogen containing esters, and from about 15% to about 75% by weight, preferably from about 20% to about 65% by weight, of substantially inert, normally liquid organic diluent. Preferably the diluent is selected from the group consisting of paraffinic oils and synthetic oils. Additive concentrates are prepared by a method comprising mixing at an elevated temperature, the foregoing ingredients, in the specified amounts,